ANZECC water quality guidelines - FAQs
11. What method of analysis should I use to determine metal & metalloid concentrations for comparison against the guidelines?
The following except from volume 2 (page 8.3-57) of the ANZECC guidelines provides useful guidance for the selection of an analytical method:
"Users may prefer to begin by measuring the total (unfiltered) metal concentration, because if this meets the guidelines then no further work is necessary (however, see cautionary notes in ANZECC & ARMCANZ [2000]). There is controversy surrounding total metal measurements and acid dissolution. From an analytical standpoint, the recovery of metals from the particulate phase will depend upon the ability of the dissolution technique to dissolve all of the metal. It can be reasonably argued that metals that are not solubilised by acid, need not be considered as having potential bioavailability. Thus, although methods have been described which measure total metals, the standard methods adopted by agencies such as the USEPA have been for acid soluble metals. These initially require sample preservation by acidification to pH <2, and then use different levels of acid treatment to measure either total recoverable metals or acid-soluble metals. Total recoverable metals are determined after digestion of the sample in a mixture of 0.15 M nitric and 0.10 M hydrochloric acids (Martin et al. 1991), while acid-soluble metals are those released by acidification to pH <2 at room temperature (Martin et al. 1991). The requirement for the rigour of the former treatment and the potential for sample contamination has been challenged (Martin et al. 1986). Recent results for acid-soluble metals have been found to be almost identical to total recoverable results (G Batley, pers. comm. 2000)."
In addition to the above, we note that:
- analysing acid soluble metals rather than total metal concentration is likely to reduce the analysis cost and is likely to be more representative of bioavailable metal concentrations and
- when analysing for aluminium the guidelines recommend undertaking a filtration step (0.45 um filter or smaller) before undertaking chemical analysis (see additional guidance in Volume 1 & 2).
Additional guidance on metal analytical methods can be found in the following sections of the ANZECC 2000 guidelines:
- Volume 1 - section 3.4.3.2 - pages 13 - 20 (specifically steps 2, 9, & 10 and figure 3.4.2) - Decision tree for applying the guideline trigger values
- Volume 2 - section 8.3 - page 102 - Metals and metalloids.
